- Email: [email protected]
Removing carbonates from silver bath
Heard on the Hotline by Ted Mooney, P.E.
Join us at http://www.finishing.com/Letters
hen we started this series of columns three years ago, it was a struggle to fill my space some months. Now I must leave out lots of interesting topics every month. So let me waste no more space in introduction. PATCHY ANODIZATION We out-source a hard coat anodize operation on a machined AA354.0 alloy. We are experiencing problems with “patchy anodization,” localized regions on the part that do not exhibit presence of an oxide layer. This seems to be localized on one region in the part. Any help to indicate where this problem can be coming from-pressure die cast or anodizing operation-will be greatly appreciated. What should be the approach in determining root cause? Ganesh Raj, [email protected] We have seen similar defects and attribute it to the residual silicone-based mold release agent. Very good degreasing prior to anodize will resolve the problem. Alternately, you may choose to change the release agent in your casting operations. Max Stein, C.P. Tech Inc., [email protected] ANODIZING
RIVETS
I need information dealing with black anodizing aluminum rivets. Has anyone tried barrel anodizing? If so, with what kind of results? Terry Bishop, [email protected] You can’t barrel anodize because the anodized surface is nonconductive and you lose contact as soon as you start. You can, however, put the rivets in a basket, squash a top onto the basket to hold all the pieces tightly in position, and then anodize in bulk. Considering the millions upon millions of rivets that are anodized, someone should probably develop a bandoleer-style anodizing machine, or other continuous anodizer, but I’ve never heard of one. Ted Mooney, Finishing Technology, N.J., [email protected] ELECTROLESS
NICKEL ON COPPER
I’m having some problems with my electroless nickel. In our line we are using a copper plate, which is covered with. 50
an electroless nickel layer (Ni-P), and afterwards with a tin-lead layer. During an aging test we are facing a problem: the nickel layer is peeling off from the copper. If you have faced similar problems or have some knowledge about this, please send me your input. Thanks in advance for your valuable help. Luis Moreno Hagelsieb, R155 l%@email.sps.mot.com We put a nickel strike on everything before applying electroless nickel. I think it helps adhesion as well as providing a catalytic surface. Bill Vins, Mesa, Ariz., [email protected] In order to assure good adhesion between copper and electroless nickel, you need to activate copper with a strike nickel or a short current in the electroless nickel solution. Sara Michaeli, Israel, [email protected]
REMOVING
CARBONATES
FROM SILVER BATH
I have a silver tank, which has an excessive carbonate level. This tank is made up using potassium carbonate, which cannot be readily removed from the tank by freezing out due to its solubility in water. I want to add calcium nitrate in small maintenance additions to lower the levels. Does anyone know the effects of the added nitrate, and at what level do nitrates cause problems with coating deposition? Robert Kestler, [email protected] We operate a 40-gal silver cyanide plating bath and have run into carbonate buildup in the past. We eliminated the carbonate problem by not returning dragout to the tank and keeping the tank at 70°F. Matt Kerby, Econco, [email protected] Potassium carbonate is fairly soluble in water (compared to sodium carbonate) so freezing out does not work. Materials such as calcium nitrate, barium cyanide, etc. will react with the potassium carbonate in the plating solution to give you a relatively insoluble carbonate. For example, barium cyanide will react with potassium cyanide to give you barium carbonate and potassium cyanide. Two ounces of barium cyanide will remove about 1.5 ounces of potassium carbonate and reform about 1.25 ounces of potassium cyanide. A word of caution here. It is a good idea to have some recent analyses of your tank so you know where you ‘&are”
0 Copyrigk; Elsevier Science Inc.
METAL FINISHING
. DECEMBER
1996
with regard to cyanide and carbonate concentrations. Test a small batch of your plating solution before charging ahead with the whole tank. Art Kushner, Kushner Electroplating School, [email protected]
HYDROGEN EMBRITTLEMENT: BLACK OXIDE?
SWITCH TO
We have had problems with a metal clip, and it is said to be due to “hydrogen embrittlement.” What is hydrogen embrittlement, and how do you avoid/alleviate it? Michael Marshall, Moll PlastiCrafters, L.P., [email protected] Hydrogen embrittlement is a phenomenon that affects high-strength steel. Hydrogen, often from pickling or plating, invades the grain structure of a high-strength steel, making it brittle and subject to catastrophic failure. The best approach is to avoid or minimize processes that cause hydrogen embrittlement. The second best approach is to bake the parts to drive the hydrogen out, preferably very soon after plating. Some people feel that some degree of permanent damage occurs during the time between plating and baking, and that it is thus vital to bake immediately. Others feel that the old standard “bake within 24 hours” is sufficient. ASTM Committee B-8 spent a lot of time on the problem this summer; I’m not sure if their conclusions are in print yet, but you might want to drop them an E-mail. Ted Mooney, Finishing Technology, N.J., [email protected] We have had some experience with the phenomenon of hydrogen embrittlement. A good reference book is “Hydrogen Embrittlement and Stress Corrosion Cracking” by Gibala and Hehemann (ASM Publication). It is quite detailed and informative. Brian Cardwell, Ford Motor Co., [email protected] I’ve been searching for black oxide specifications, particularly relating to coating of fasteners. I’ve found a general AMS black oxide specification. My company is moving away from zinc plating due to hydrogen embrittlement issues and we need to specify the appropriate black oxide processes. Do you have any suggestions? Mike Scheller, Fluid Management, [email protected]
specification instead of AMS 2485, 1. Use Mil-C-13924 there are better controls in the Military specification and it provides details on correct processing for different materials. 2. Do not use acid cleaning for high-strength steels; vapor blast is effective for cleaning and surface preparation. 3. Require a magnetic particle inspection (MPI) after the black oxide process. 4. Oiling of the surface is required after black oxide; this oil must be removed to allow effective MPI and then the oil reapplied after inspection to assure corrosion protection. 5. Acid stripping and recoating cycles will compound a hydrogen embrittlement problem since the part is exposed to the acid longer. 6. Use hooks and fixtures made of iron or steel, and mask parts of assemblies that are not ferrous material to prevent corrosion contamination of the bath. 7. The black oxide processing time must be closely controlled to prevent intergranular attack (IGA) and alkaline embrittlement. Melissa Parks, GE Aircraft Engines, [email protected]
JELLYING
CONCENTRATED
ACIDS
Note from Ted Mooney: The policy of this column is to attribute all questions and answers. But this particular question has such severe safety implications that it absolutely must he addressed, while at the same time, we don’t want to embarrass the inquirer, so his name has been withheld. I’m looking for a chemical compound that allows jellying a mixture of concentrated nitric and hydrofluoric acids. Anonymous Like napalm, this stuff might not be usable except under VERY controlled conditions. What will inevitably happen is that someone will start sloshing this mixture onto vertical surfaces without the proper safety precautions, and someone, usually a bystander, will get injured. Also, hydrofluoric acid is absorbed through the skin (and from under fingernails), the fluoride reacts with calcium in your bones-it’s not a pretty scenario. Find another way! By the way, napalm gets its name from NAphthene PALMitate, a mixture of aluminum soaps used in jellying gasoline. Tom Pullizzi, Team*Faraday, Inc., [email protected]
Here are some specification numbers: ASTM D 769, AMS 2485, MIL-C-13924, MIL HDBK 205--there are others too. Switching to black oxide should be helpful toward avoiding hydrogen embrittlement, but remember that the corrosion resistance of black oxide does not compare to zinc plating! Ted Mooney ([email protected]) Finishing Technology, N.J.
Having worked in the plating industry for 29 years, there is only one material our industry uses that truly frightens me: hydrofluoric acid. If any reader does not share my concern, please subscribe to the Internet scientific newsgroup sci.chem and read the horror stories. Like Tom, I find the idea of jellied hydrofluoric acid terrifying, and urge people to not even consider using it. Ted Mooney, Finishing Technology, N.J., [email protected]
There is still the potential Some guidelines:
Kinnelon,
METAL FINISHING
.
for hydrogen
DECEMBER
1996
embrittlement.
Ted Mooney is an independent consulting engineer based in N.J. MF
51
Join us at http://www.finishing.com/Letters
hen we started this series of columns three years ago, it was a struggle to fill my space some months. Now I must leave out lots of interesting topics every month. So let me waste no more space in introduction. PATCHY ANODIZATION We out-source a hard coat anodize operation on a machined AA354.0 alloy. We are experiencing problems with “patchy anodization,” localized regions on the part that do not exhibit presence of an oxide layer. This seems to be localized on one region in the part. Any help to indicate where this problem can be coming from-pressure die cast or anodizing operation-will be greatly appreciated. What should be the approach in determining root cause? Ganesh Raj, [email protected] We have seen similar defects and attribute it to the residual silicone-based mold release agent. Very good degreasing prior to anodize will resolve the problem. Alternately, you may choose to change the release agent in your casting operations. Max Stein, C.P. Tech Inc., [email protected] ANODIZING
RIVETS
I need information dealing with black anodizing aluminum rivets. Has anyone tried barrel anodizing? If so, with what kind of results? Terry Bishop, [email protected] You can’t barrel anodize because the anodized surface is nonconductive and you lose contact as soon as you start. You can, however, put the rivets in a basket, squash a top onto the basket to hold all the pieces tightly in position, and then anodize in bulk. Considering the millions upon millions of rivets that are anodized, someone should probably develop a bandoleer-style anodizing machine, or other continuous anodizer, but I’ve never heard of one. Ted Mooney, Finishing Technology, N.J., [email protected] ELECTROLESS
NICKEL ON COPPER
I’m having some problems with my electroless nickel. In our line we are using a copper plate, which is covered with. 50
an electroless nickel layer (Ni-P), and afterwards with a tin-lead layer. During an aging test we are facing a problem: the nickel layer is peeling off from the copper. If you have faced similar problems or have some knowledge about this, please send me your input. Thanks in advance for your valuable help. Luis Moreno Hagelsieb, R155 l%@email.sps.mot.com We put a nickel strike on everything before applying electroless nickel. I think it helps adhesion as well as providing a catalytic surface. Bill Vins, Mesa, Ariz., [email protected] In order to assure good adhesion between copper and electroless nickel, you need to activate copper with a strike nickel or a short current in the electroless nickel solution. Sara Michaeli, Israel, [email protected]
REMOVING
CARBONATES
FROM SILVER BATH
I have a silver tank, which has an excessive carbonate level. This tank is made up using potassium carbonate, which cannot be readily removed from the tank by freezing out due to its solubility in water. I want to add calcium nitrate in small maintenance additions to lower the levels. Does anyone know the effects of the added nitrate, and at what level do nitrates cause problems with coating deposition? Robert Kestler, [email protected] We operate a 40-gal silver cyanide plating bath and have run into carbonate buildup in the past. We eliminated the carbonate problem by not returning dragout to the tank and keeping the tank at 70°F. Matt Kerby, Econco, [email protected] Potassium carbonate is fairly soluble in water (compared to sodium carbonate) so freezing out does not work. Materials such as calcium nitrate, barium cyanide, etc. will react with the potassium carbonate in the plating solution to give you a relatively insoluble carbonate. For example, barium cyanide will react with potassium cyanide to give you barium carbonate and potassium cyanide. Two ounces of barium cyanide will remove about 1.5 ounces of potassium carbonate and reform about 1.25 ounces of potassium cyanide. A word of caution here. It is a good idea to have some recent analyses of your tank so you know where you ‘&are”
0 Copyrigk; Elsevier Science Inc.
METAL FINISHING
. DECEMBER
1996
with regard to cyanide and carbonate concentrations. Test a small batch of your plating solution before charging ahead with the whole tank. Art Kushner, Kushner Electroplating School, [email protected]
HYDROGEN EMBRITTLEMENT: BLACK OXIDE?
SWITCH TO
We have had problems with a metal clip, and it is said to be due to “hydrogen embrittlement.” What is hydrogen embrittlement, and how do you avoid/alleviate it? Michael Marshall, Moll PlastiCrafters, L.P., [email protected] Hydrogen embrittlement is a phenomenon that affects high-strength steel. Hydrogen, often from pickling or plating, invades the grain structure of a high-strength steel, making it brittle and subject to catastrophic failure. The best approach is to avoid or minimize processes that cause hydrogen embrittlement. The second best approach is to bake the parts to drive the hydrogen out, preferably very soon after plating. Some people feel that some degree of permanent damage occurs during the time between plating and baking, and that it is thus vital to bake immediately. Others feel that the old standard “bake within 24 hours” is sufficient. ASTM Committee B-8 spent a lot of time on the problem this summer; I’m not sure if their conclusions are in print yet, but you might want to drop them an E-mail. Ted Mooney, Finishing Technology, N.J., [email protected] We have had some experience with the phenomenon of hydrogen embrittlement. A good reference book is “Hydrogen Embrittlement and Stress Corrosion Cracking” by Gibala and Hehemann (ASM Publication). It is quite detailed and informative. Brian Cardwell, Ford Motor Co., [email protected] I’ve been searching for black oxide specifications, particularly relating to coating of fasteners. I’ve found a general AMS black oxide specification. My company is moving away from zinc plating due to hydrogen embrittlement issues and we need to specify the appropriate black oxide processes. Do you have any suggestions? Mike Scheller, Fluid Management, [email protected]
specification instead of AMS 2485, 1. Use Mil-C-13924 there are better controls in the Military specification and it provides details on correct processing for different materials. 2. Do not use acid cleaning for high-strength steels; vapor blast is effective for cleaning and surface preparation. 3. Require a magnetic particle inspection (MPI) after the black oxide process. 4. Oiling of the surface is required after black oxide; this oil must be removed to allow effective MPI and then the oil reapplied after inspection to assure corrosion protection. 5. Acid stripping and recoating cycles will compound a hydrogen embrittlement problem since the part is exposed to the acid longer. 6. Use hooks and fixtures made of iron or steel, and mask parts of assemblies that are not ferrous material to prevent corrosion contamination of the bath. 7. The black oxide processing time must be closely controlled to prevent intergranular attack (IGA) and alkaline embrittlement. Melissa Parks, GE Aircraft Engines, [email protected]
JELLYING
CONCENTRATED
ACIDS
Note from Ted Mooney: The policy of this column is to attribute all questions and answers. But this particular question has such severe safety implications that it absolutely must he addressed, while at the same time, we don’t want to embarrass the inquirer, so his name has been withheld. I’m looking for a chemical compound that allows jellying a mixture of concentrated nitric and hydrofluoric acids. Anonymous Like napalm, this stuff might not be usable except under VERY controlled conditions. What will inevitably happen is that someone will start sloshing this mixture onto vertical surfaces without the proper safety precautions, and someone, usually a bystander, will get injured. Also, hydrofluoric acid is absorbed through the skin (and from under fingernails), the fluoride reacts with calcium in your bones-it’s not a pretty scenario. Find another way! By the way, napalm gets its name from NAphthene PALMitate, a mixture of aluminum soaps used in jellying gasoline. Tom Pullizzi, Team*Faraday, Inc., [email protected]
Here are some specification numbers: ASTM D 769, AMS 2485, MIL-C-13924, MIL HDBK 205--there are others too. Switching to black oxide should be helpful toward avoiding hydrogen embrittlement, but remember that the corrosion resistance of black oxide does not compare to zinc plating! Ted Mooney ([email protected]) Finishing Technology, N.J.
Having worked in the plating industry for 29 years, there is only one material our industry uses that truly frightens me: hydrofluoric acid. If any reader does not share my concern, please subscribe to the Internet scientific newsgroup sci.chem and read the horror stories. Like Tom, I find the idea of jellied hydrofluoric acid terrifying, and urge people to not even consider using it. Ted Mooney, Finishing Technology, N.J., [email protected]
There is still the potential Some guidelines:
Kinnelon,
METAL FINISHING
.
for hydrogen
DECEMBER
1996
embrittlement.
Ted Mooney is an independent consulting engineer based in N.J. MF
51